The noble metal platinum commonly is used in fuel-cell cathodes as an electrocatalyst for the oxygen-reduction reaction (ORR). However, the need for large amounts of costly platinum remains an economic hindrance in the development of fuel cells for large-scale implementations such as in automobiles, for example. Fuel-cell catalysts typically comprise nanoparticles of platinum or of catalytically active platinum alloys. The nanoparticles may be supported on a material such as carbon.
To reduce the amount of platinum required in fuel cells, catalysts may be developed to have higher platinum mass activities. The platinum mass activity is a function of electrocatalytic activity per mass amount of platinum, irrespective of the presence of other metals in the catalyst. As such, in comparing a pure-platinum catalyst (100% platinum) and a platinum-alloy catalyst (less than 100% platinum) having all other physical and catalytic properties identical and being loaded to the same amount onto a catalyst support, the platinum-alloy catalyst may have a higher platinum mass activity than that of the pure-platinum catalyst. In this regard, binary and ternary platinum-nickel alloys and platinum-cobalt alloys are of particular interest.
Increased platinum mass activity of a given platinum-alloy nanoparticle catalyst can be attained, for example, through control of the composition, shape, and particle size of the nanoparticles used for the catalyst. With particular regard to shape, it has been recognized that catalytic activity of certain platinum alloys may be enhanced when the catalytic surface has a (111)-orientation, as opposed to a (100)-orientation. However, common synthetic methods for platinum-alloy nanoparticles typically lead to spherical nanoparticles. Attempts at preparing platinum-alloy nanoparticles with (111)-faceted surfaces have involved high reaction temperatures (above 500° C.), undesirable reagents such as toxic solvents or reagents, and/or very powerful reducing agents, and/or time-consuming and expensive plasma surface-treatments to clean the particle surfaces. Ongoing needs exist for efficient methods to produce platinum-alloy nanoparticles with increasing catalytic activity.